Fillets?

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I mask off the fin, apply the epoxy and "pull" it with a tongue depressor. After waiting a few minutes, I remove the tape. If their are any imperfections, a I fill them with filler.
 
Are the holes from bubbles? Is there a way to avoid this? Or a good way to fill them after the first coat is dry?

Never tried the tongue. Tried a depressor. Will try licking them and see if that works though.

West System is notorious for capturing air when you use additives. Some people say beat the heck it out of it but I've only found this to add more air. When I was still using West for fillets, I ended up doing tons of stirring (like 20 minutes) fairly slowly back and forth. This seemed to reduce trapped air overall, but you still got at least a small amount of those stinking bubbles. What worked better was to allow some setting of the epoxy, say 30+ minutes, and then apply low heat with a heat gun. Use a low fan setting if possible as you may blow the epoxy right out of the root edge. In just a few seconds as surface of the epoxy warms, you should see bubbles moving to the top "skin" and popping; the bubble locations should then smooth out.

On the fillets that are already mostly cured, you can fill those easily with any epoxy filler like SuperFil or even Bondo putty.
 
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You will not get a perfectly smooth finish with collodial silica however it does sand easily. You have a couple of choices. You could add another thin layer of epoxy with no additives after masking and what not. You can sand what you have and then brush on a mayonnaise consistency wood filler then sand again. You can also use bondo brand glazing putty.

I built my Dark Star Jr. with West Systems and collodial silica as the additive. This was my first fiberglass build that I did not use "hobby epoxy" on. I had the same problem. I went with the sanding and then brushing on wood filler and the fillets came out nice. Not perfect, but nice. I have since gone back sanded off the paint and used the glazing putty to get the fillets perfect.

On my builds now I use micro balloons instead of collodial silica as the additive. Strangely enough, the Collodial works well as a filler with hobby epoxy. I now use micro balloons on the outside fillets and I get a perfect fillet, just requires some sanding and filling.

Did you do anything for internal fillets?
 
Brad (and Adam) -

That comment about doing a search is actually not directed at you. It's part of my signature and therefore appears at the bottom of all my posts. It's actually directed at "those people" who always seem to scream "DO A SEARCH" every time someone posts a question on forums. Apologies if you felt it came off as a semi-rude comment meant for you.

And the tongue comment was actually a playful barb for Scotty Dog. I'm pretty sure you got the jest (please do not lick uncured epoxy!)

So now to taking your requests seriously.....

Yeah, air bubbles. They can be a pain. The first thing to do is to perhaps mix a bit less filler in your epoxy next time. That way any air bubbles that do get mixed in have a better chance of rising and popping before stuff cures. You could also let your mixed epoxy sit for longer (assuming you keep an eye on cure times), and let the air bubbles rise and pop before laying actual fillets. When you mix your epoxy and also when you mix in any filler, go for a slower smoother approach and try not to introduce so many small bubbles into the mix in the first place. Next, some folks have had luck applying heat to the fillets before they cure to encourage the bubbles to rise out. You can also use a pin or somesuch to pop them before curing hard. Lastly, if you do still end up with holes at the surface of your cured fillets, you can use any type of filler (I use bondo) and sand them smooth when dried.

As a side note, I've used many different epoxies and fillers in the past. No matter what product or process I use, if I want REALLY nice, smooth fillets - or if I'm shooting for a "flawless" finish - sanding them down after curing is pretty much required. They will all bubble or bulge or come out rough to some degree - some more than others, but it's part of the game no matter what. I use a short length of PVC pipe to shape my fillets when laying them (dipped in alcohol as you do), and then I use the same piece wrapped in sandpaper to smooth them once cured if I'm going for a high quality finish.

Good luck honing your technique, apologies again if my earlier comments came off as rude, and POST SOME PICs of your work!

s6
 
Ah, answers I can use. Will try to slow down and do more smoothing on the next batch and resign myself to a little post fillet work.

Also no hard feelings on the comments. Sometimes it's frustrating, or more frustrating when already frustrated by a build, when the first response is not much help at all.

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OUCH!!! What a DH!
 
Ok, this may cause some to laugh, but I was having issues with previous rockets having brittle fillets and they would either separate from the body tube or crack. I was scratch building 4" dia. test bed generic rocket, about 3 lbs., which would use 38MM mount and likely a I-161 motor or larger. It would be about average on speed etc.. I was trying to figure out something to make fillets with, that would adhere well, be paint-able, be a little bit flexible, have easy application and clean up and be cheap. I looked on my pegboard and saw a new tube of DAP, Dynaflex 2320 caulking. It met all of my criteria. I made a test piece out of an old piece of body tube and 1/4" glassed plywood. It was super easy to make a perfect fillet, cleaned up with water. I used filler primer and yellow from a rattle can from Rustoleum.

I have flown that rocket many, many times, with H-I motors and the fillets look like new. They turned out better than anything else I have tried.

Of course, this was a quick throw together rocket. But since then I have used this method several times on "prettier" rockets that flew faster and used better paint; so far, so good!! Anyway, just thought I'd mention an out of the box idea...Cheers!!

Click image for larger version. Name: Caulk.jpg Views: 42 Size: 76.1 KB ID: 178824

Caulk.jpg
 
Another note: smooth out your fillets as you are laying them with a piece of PVC about 1-1.5 inches in length dipped in Denatured Alcohol can help smooth them out as well. I also from time to time depending on the size of the rocket use the tip of a plastic spoon.
 
... Tips to get much smoother fillets that need way less attention after hardening???

Have you asked Gougeon Bros? Their support is pretty good.

They mfg 6 different fillers/blends with different properties for different purposes.
 
Here is what I do, though I only used hobby epoxy, it should work.

Take a dowel that has the circumference you want for the fillet. Place a piece of carbon copy paper or graphite paper (Michaels) over the fillet area and drag the end of the dowel at an angle across the fillet area. Then mask up to the lines created by the paper and pour your glue. Then place wax paper over it and lay the dowel on top and wipe off any abundant excess. I use rubber bands to fold down the dowels. Then remove the wax paper and mask when hard enough it will hold it's shape. I then use Bondo glaze and spot to take care of any holes/divets.
 
Ah, answers I can use. Will try to slow down and do more smoothing on the next batch and resign myself to a little post fillet work.

Also no hard feelings on the comments. Sometimes it's frustrating, or more frustrating when already frustrated by a build, when the first response is not much help at all.


Not a dig at anyone.

And yet, it was a dig at someone specific.
 
"Anyone" means exactly that. Anyone. Not someone. Don't try to read more into it. Just good to get answers. This forum is sometimes hard to navigate. And is sometimes frustrating when you want a specific answer to a specific problem. If it was a dig at anything it was the search feature and how useless it can be.

When you said "the first response is not much help at all" it was a dig at that specific person. And that is why he (ScottyDog) was offended. What is worse, replies that aren't helpful in your opinion, or people who are offensive?
 
+1 on the micro balloons. Makes sanding much easier.


... On my builds now I use micro balloons instead of collodial silica as the additive. Strangely enough, the Collodial works well as a filler with hobby epoxy. I now use micro balloons on the outside fillets and I get a perfect fillet, just requires some sanding and filling.
 
I use parchment paper and that works well for me. I haven't found anything that will stick to it and you can re-use it.

H... Then place wax paper over it and lay the dowel on top and wipe off any abundant excess.
 
Just an idea that might suck. But it would seem that if you use a pump to measure, perhaps you could add the filler to the epoxy before the hardener is added. Then stir and let sit for bubbles to rise. Potentially, one could pull a vacuum to get bubbles out before adding the hardener.



Kirk
 
Just an idea that might suck. But it would seem that if you use a pump to measure, perhaps you could add the filler to the epoxy before the hardener is added. Then stir and let sit for bubbles to rise. Potentially, one could pull a vacuum to get bubbles out before adding the hardener.



Kirk

Not a good idea, the very small particles of filler will have resin on the surround and it may not mix well with the hardener later.
 
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